DLM: Energy Balance, Obesity and Anthropometric Measurement (2005)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To examine the relationship of obesity, measured as BMI and weight change to incidence of coronary heart disease (CHD) among women with diabetes.

Inclusion Criteria:

Women with Type 2 diabetes, who were in the Nurses’ Health Study.

Exclusion Criteria:

Cardiovascular disease (CVD) or cancer at the beginning of the follow-up period.

Description of Study Protocol:
  • BMI values were measured three times:
    • At age 18, in 1976 and the present from reported height and weight
    • Women reported cases of CHD every two years
  • These were confirmed by medical record review.

Anthropometrics

  • Height measured: Yes
  • Weight measured: Yes
  • Fat-free mass measured: No
  • BMI measured: Yes.

Statistical Tests 

  • The relative risk (RR) was calculated as the rate for a given category of BMI or weight change as compared with the referent category
  • Age-adjusted analyses were conducted using five year age categories
  • Pooled logistic regression was used to adjust for age or other potential cofounders. This has been shown to be similar to Cox proportional hazard regression with time-varying covariates.
  • 95% CI were calculated
  • All P-values were two-sided. 
Data Collection Summary:

Blinding used: No.

Description of Actual Data Sample:

N=5,897 females.

Summary of Results:
  • There were 236 cases of nonfatal MI and 182 cases of fatal CHD
  • The multivariate risks across increasing categories of BMI had a trend that was significant, P<0.001
  • Weight gain before the diagnosis of diabetes was related to increased risk of CHD
  • In contrast, weight gain after diagnosis was not associated with risk of CHD. 

Multivariate Analysis Among Women Who Developed Diabetes Between 1976 to 1994

BMI (kg per m2)

RR

20-22.9

1.00

23-24.9

1.58

25-26.9

1.85

27-29.9

1.95

30-34.9

2.80

>35

3.21

P-value for trend <0.001.

Multivariate Analysis Among Women with Existing Diabetes in 1976

BMI  (kg per m2)

RR

20-22.9

1.00

23-24.9

1.12

25-26.9

1.70

27-29.9

1.67

30-34.9

3.10

>35

2.44

P-value for trend <0.001.

Adjusted for age, smoking, use of hormone replacement therapy post-menopausal, parental history of MI before age 60, duration of diabetes, insulin or other hypoglycemic treatment and time period.

Author Conclusion:

After adjustment for age, smoking and other coronary risk factors, current BMI was strongly associated with increased risk of CHD among diabetic women.

Funding Source:
Government: NIH
University/Hospital: Harvard School of Public Health, Harvard Medical School, Brigham and Women's Hospital
Not-for-profit
0
Foundation associated with industry:
Reviewer Comments:

Strengths

  • Strong power with large sample size
  • Credible use of statistics.

Generalizability/Weaknesses 

  • The criteria for diagnosis of diabetes was the old National Diabetes Group criteria. Had new standards been applied, the subjects would have increased.
  • Small number of minorities, so no separate analysis.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) N/A
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) N/A
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? N/A
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? N/A
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes